Inulavosin, a Melanogenesis Inhibitor, Leads to Mistargeting of Tyrosinase to Lysosomes and Accelerates its Degradation

Abstract

The melanosome is a highly specialized organelle where melanin is synthesized. Tyrosinase and tyrosinase-related protein-1 (Tyrp1) are major melanosomal membrane proteins and key enzymes for melanin synthesis in melanocytes. Inulavosin, a melanogenesis inhibitor isolated from Inula nervosa (Compositae), reduced the melanin content without affecting either the enzymatic activities or the transcription of tyrosinase or Tyrp1 in B16 melanoma cells. To our knowledge, this inhibitor is previously unreported. Electron-microscopic analyses revealed that inulavosin impaired late-stage development of melanosomes (stages III and IV), in which melanin is heavily deposited. However, it did not alter the early stages of melanosomes (stages I and II), when filamentous structure is observed. Immunofluorescence analyses showed that tyrosinase, but not Tyrp1, was specifically eliminated from melanosomes in cells treated with inulavosin. Unexpectedly, inulavosin specifically accelerated the degradation of tyrosinase but not other melanosomal/lysosomal membrane proteins (Tyrp1, Pmel17, and LGP85). The degradation of tyrosinase induced by inulavosin associated with lysosomes but not the proteasome. Interestingly, lysosomal protease inhibitors restored the melanogenesis but not the targeting of tyrosinase to melanosomes in the cells treated with inulavosin. Instead, colocalization of tyrosinase with lysosome-associated membrane protein-1 at late endosomes/multivesicular bodies and lysosomes was accentuated. Taken together, inulavosin inhibits melanogenesis as a result of mistargeting of tyrosinase to lysosomes.

Combining poly-arginine with the hydrophobic counter-anion 4-(1-pyrenyl)-butyric acid for protein transduction in transdermal delivery

“…Melanin content was measured described previously [19]. Briefly, B16-4A5 cells dissolved in 1ml of 5% Trichloroacetic acid (TCA) were incubated on ice for 10 min.…”

First synthesis of 2‐(2,4,4‐trimethyl‐3,4‐dihydro‐2H‐benzo[h]chromen‐2‐yl)‐1‐naphthol and 3‐(2,4,4‐trimethyl‐3,4‐dihydro‐2H‐benzo[g]chromen‐2‐yl)‐2‐naphthol from 1‐ and 2‐naphthol derivatives

“…5) 3 , is reported in literature [13] but with no spectroscopic data. Hence it was characterized by its spectral data and is included in the Experimental section.…”

“…To our knowledge there is only one report on a naturally occurring flavan of this type called inulavosin [2-(2 0 -hydroxy)-2,4 0 ,4,4,7-penta methyl flavan] isolated [2] from Inula nervosa (Compositae) having piscicidal activity [2] and recently discovered as a melanogenesis inhibitor [3]. The flavan inulavosin is a dimer of thymol and was prepared [4] from m-cresol and acetone much before its isolation as a natural product.…”

1-(2,4-Dihydroxyphenyl)-3-(2,4-dimethoxy-3-methylpheny)propane inhibits melanin synthesis by dual mechanisms

“…Hall et al stated that phenylthiourea promotes tyrosinase degradation following maturation in the Golgi apparatus in an endosomal/lysosomal cysteine proteasome-dependent manner in cultured melanocyte [30]. Fujita et al reported that inulavosin, a melanogenesis inhibitor, accelerates tyrosinase degradation by mistargeting of tyrosinase to lysosomes [17]. Those reports demonstrate that manipulating the balance between tyrosinase synthesis and degradation is quite capable of modifying melanogenesis.…”

“…by the ubiquitin-mediated proteasome pathway [11,[13][14][15][16] and the lysosomal pathway [17]. Similar to other proteins, a balance between synthesis and degradation modulates the intracellular protein level of tyrosinase.…”